Syrian security forces killed at least 62 people in an escalation of the crackdown on protests ahead of the Muslim holy month of Ramadan, according to activists and residents.

Most died in raids on the flashpoint city of Hama yesterday, where a barrage of shelling and gunfire left bodies scattered in the streets.

Protests calling for President Bashar Assad's ousting are expected to swell during Ramadan, which starts Monday, in Syria.

Security forces appeared to be racing against time as they stormed cities and small villages across the country in an attempt to crush a remarkably resilient uprising that began in mid-March.

Having sealed off the main roads into the opposition stronghold of Hama almost a month ago, army troops in tanks pushed into the city from four sides before daybreak today in a co-ordinated assault.

Residents shouted "God is great!" and threw firebombs, stones and sticks at the tanks.

The crackle of gunfire and thud of tank shells echoed across the city, and clouds of black smoke drifted over rooftops.

"It's a massacre. They want to break Hama before the month of Ramadan," a man called Ahmed, said by telephone from Hama, where at least 49 people were killed.

Hospitals were overwhelmed with casualties and were seeking blood donations, he said.

Foreign Secretary William Hague said the attacks against civilians were "all the more shocking" on the eve of Ramadan and appeared to be part of a "co-ordinated effort to deter Syrians" from protesting during Ramadan.

"President Bashar is mistaken if he believes that oppression and military force will end the crisis in his country.

"He should stop this assault on his own people now," Mr Hague said.

During Ramadan, Muslims throng mosques for special night prayers after breaking their daily dawn-to-dusk fast.

The gatherings could trigger intense protests throughout the predominantly Sunni country and activists say authorities are moving to ensure that does not happen.

Other raids were reported in southern Syria and in the suburbs of the capital Damascus.

In the neighbourhood of al-Joura in the eastern city of Deir el-Zour, soldiers in tanks fired machine guns, killing at least seven people, activists said.

An estimated 1,600 civilians have died in the crackdown on the largely peaceful protests against President Assad's regime since the uprising began.

Most were killed in shootings by security forces on anti-government rallies.